1. Field of the.Invention
The present invention lies in the field of weld pins and more particularly to resistance weld pins used for attaching batts or sheets of insulated material to the interior surfaces of air ducts such as the ducts of air conditioning and heating systems.
2. The Prior Art
It is known to improve the energy efficiency of air conditioning and heating installations which employ metallic duct work, to apply to the ducts, and normally to the interior portions thereof, batts or sheets of insulating material. The insulation is typically one to two inches thick and comprised of a layer of fibrous material such as fiberglass.
The insulation is typically connected to the duct by an adhesive. In order to assure permanence of connection, a plurality of metallic members having a head portion bearing against the exposed surface of the insulation has a free end portion welded or otherwise attached to the metal duct.
A typical attachment mode employs a pin having an enlarged head and a sharpened tip. A washer is sleeved under the head to provide a large contact area with the insulation. The pin is applied by effecting a resistance weld between the sharpened tip and the interior of the duct, the pin having been forced through the insulation to provide contact between the tip and duct. A current is passed through the length of the pin while the pin is urged toward the duct resulting in the melting of the tip adjacent portions of the pin fusing the pin, to the duct.
Representative examples of pins for connecting insulation to ducts are found in the following U.S. Pat. Nos.: 4,855,561; 4,855,562; 3,582,603; 3,624,340; 3,835,285; 3,858,024; 4,438,314; 4,482,795; 4,614,855; 4,429,209; 4,031,350; 3,701,878; 3,624,340; 3,591,763; and 3,591,762. The above patents are owned by the Assignee of the instant application.
A difficulty inherent in the use of conventional weld pins as described above has been observed. Over time, the moving air stream within the duct has eroded the soft insulation material surrounding the pin heads. The erosion has caused increments of the insulation to become separated from the main mass and carried by the air stream through the ducting and injected into the treated environment. In addition, conventional pins have caused significant turbulence in the air stream resulting in reduced efficiency of air flow.
The present invention may be summarized as directed to a resistance weld pin having improved aerodynamic qualities. More particularly, it has been discovered that by modifying the configuration of the washer from the conventional simple planar disk in the manner set forth hereinbelow, erosion of the insulation material is minimized and the drag of frictional flow resistance is reduced.
In accordance with the invention there is provided a resistance weld pin having a shank, at one end of which is formed an enlarged head and at the other end a sharpened tip. A washer is sleeved over the tip along the shank into contact with the undersurface of the head of the weld pin. A characterizing feature of the invention resides in the configuration of the washer. More particularly, the washer includes a depression within which the head of the pin resides, the upper surface of the pin head lying in a plane above the depression. Surrounding the depression is a planar platform annulus, and surrounding the annulus is a well or trough extending between the platform and the outer margin of the washer.
The washer configuration described has provided a weld pin with substantially reduced tendency to create a turbulence adjacent the washer, which ultimately results in increments of the insulation being introduced into the air stream. In addition, the fluid flow within the duct has been improved. The significance of improved flow will be best appreciated when it is recognized that certain installations may include thousands of weld pins.
It is accordingly an object of the invention to provide a resistance weld pin for securing insulation to duct work which has aerodynamic characteristics superior to insulation pins heretofore known.
A further object of the invention is the provision of a resistance weld pin for supporting insulation to duct interiors, which is resistant to erosion of the pin adjacent components of insulation.
A still further object of the invention is the provision of a weld pin having a washer component which deflects air currents away from the insulation and into the central air stream.